Means for suppressing noise in radio receivers



Nov. 21; 1939.

P. M. HAFFCKE MEANS FOR SUPPRESSING NOISE IN RADIO RECEIVERS Filed NOV.5, 1957 AmplQQr 9 1 Ion Jahear 4mph; Ler

Ky U A A INVENTOR PhilipMHaffcke v ATTORNEY Patented Nov. 21, 1939UNITED STATES MEAN S FOR. SUPPRESSING NOESE 1N RIO RECEIVERS 9 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 376) 0. G. 757) This invention relates to thesuppression of noise in radio receivers, such as that due to thephenomenon commonly called static, and has among its several objects:

To provide means responsive to excessive surges of energy interceptableby a radio receiver to modify the plate or accelerating grid voltageproportionally to the excess amplitude of the energy and in a manner tooffset the effects thereof;

Toprovide means for so modifying the form of the output wave of areceiver stage, in response to static surges, that the static affectedportion of the wave is substantially excluded by the following stages;

To provide means for controlling the effect of static, which means issimple to apply to existing receivers and does not necessitaterealigning of the set;

To provide means for effectively reducing the effect of static withoutcausing impulse excitation in the following stages.

In the drawing:

Fig. 1 illustrates diagrammatically a circuit embodying my presentinvention wherein static control is achieved by reducing the platevoltage;

Fig. 2 depicts my invention applied to control the voltage on theaccelerating grid of a vacuum tube;

30 Figs. 3 to 7 show various wave forms and amplitudes involved in thepractice of the present invention, all of which will be explained indetail hereinafter.

It is known that noise suppression may be 35 effected by applying to agrid immersed in the electron stream, the noise component on a signalchannel, whereby the signal circuit is interrupted, or thetransconductance of a tube altered.

I find that the interruption for the duration of extreme surges may beaccomplished by still another means and with the further advantage, thatwhen desired this apparent interruption may be brought about withoutapparent shock, or rapid change of plate current, which would causeimpulse excitation in the following tuned circuits in the output of thestage and in following stages.

Noise-control may-be effected by interrupting the path between theoscillator and the mixer stage for the oscillator frequency used forhetero- 50 dyning, or frequency changing, but the connections requiredfor this will requireexperts for installation who are equipped forrebalancing of the tuning circuits, because such oscillators are usuallytuned by a variable condenser which is ganged withthe condensers usedfor tuning the signal frequency channel, and molesting the circuits ofthe oscillator throws those circuits badly out of tune by the addedcapacity afforded by even short lengths of wire. I However, if a tubecan be placed in the path- 5 of oscillator frequency and be interruptedwithout requiring such retuning operations, or if any one of the RF(either TRF or IRF) circuits can be broken, or the tubes madeinoperative withp out a rapid change in current flow, then the 10chances of shock excitation are reduced'to a ,desirable minimum and thechances of reducing the effects of atmospherics without secondary shockeffects nearly as bad as the static itself, H become a reality. 16

The system herein proposed provides a method of accomplishing this byreducing the Ep of the stage to be affected, to either a low momentaryvalue, or zero to even slightly negative in periods of excessive surges.By this method of plate :20 voltage control, and'by biasing theaffected-tube to a point where the Eg-Ip is approximately zero during nosignal periods, there can be very little or no change in the platecurrent in the output circuits of the tube when interrupting 1 5 thesignal channel. However, if the output of the tube is sharply tuned, itsresponse can be reduced almost to zero due to the peculiar form of theWave delivered thereto. 7

Referring to Fig. 1, the tube 8 is of standard form and may be in eithera tuned radio frequency stage, an intermediate radio frequency stage, anaudio-frequency stage, or it may even be a detector. The output of thepreceding stage is indicated by primary 9 of transformer i0 whereof thesecondary M is connected to grid [2 and cathode it in the input circuitof tube 8. The plate I4 of tube 8 is connected to a source of positivepotential through a series resistance l5 that is also in series withanode l5 and cathode ll of a diode rectifier l8. Connected to the signalchannel ahead of primary 9 is a non-linear amplifier l9 that willdisproportionately amplify signal components that are of greater thanpredetermined amplitude and the output of this amplifier is coupledthrough primary 20 to secondary 2! in the anode-cathode circuit ofrectifier it. It will be apparent to those skilled in the art that theeffect of a normal signal upon rectifier l8 will be negligible butuponthe arrival of excessive surges in a static affected signal therectifier M3 will be caused to pass a large current that will traverseresistance l5 and impress upon plate M a voltage drop proportional .tothe current flowing and in opposition to the constant positive voltageimpressed upon the plate, thereby reducing or even stopping entirely theflow of current in the output circuit of tube 8. It is apparent that thenormal plate voltage should be adjusted to such value that the IR dropacross resistance I5 will, during excessively heavy surges, completelybuck out the normal plate voltage or in some instances actually changethat voltage to a negative value. The amplifier I 9 may readily be sodesigned as to cause the rectifier I8 to secure the results mentionedeven though the normal plate voltage be of the order of 250 volts ormore.

The circuit depicted in Fig. 2 is in general similar to that abovedescribed and the elements therein that are common to the two have beendesignated by the same reference characters. However, the method ofcontrol is somewhat different. The grid 22 in this figure is normallymaintained at a suitable positive voltage to accelerate the passage ofelectrons from cathode l3 to plate I4 and is termed an acceleratinggrid. It will be seen that reducing the positive voltage on grid 22 orchanging that voltage from a positive to a negative value will exert astrong controlling influence on the electron stream in the tube andtherefore the IR drop due to current from rectifier l8 passing throughresistance 23 is applied to oppose the normal positive voltage onaccelerating grid 22. Instead of obtaining the entire voltage dropacross resistance 23,-an inductance 24 having a suitable impedance tocause the desired drop may be used therewith to secure certainbeneficial results that follow therefrom, or the resistance 23 may beomitted and the entire drop be secured across the inductive impedance.The inductance 24 may be by-passed by a condenser 25. It is of courseunderstood that all circuit elements are sochosen as to provide thedesired time constants in the circuit. The voltage applied to grid 22will drift from positive values of, say, 1 to 250 volts, to possibly 200volts negative. When the constant voltage applied to grid 22 is on theorder of 25 volts positive it will act as an eflicient accelerator ofthe electrons and allow the tube to reproduce normal signals but when itdrifts to a strong negative polarity it will act as a rapid cutoff forthe plate current and will create harmonics in the output circuitearlier than might be possible by plate voltage control only when thatplate voltage is quite high.

Fig. 3 shows at a the wave amplitude of a normal signal and at b anassumed amplitude of an excessive surge that might be impressed upon thecontrol grid 12, which excessive amplitude it is desired to suppress.

Fig. 4 shows at c and d the normal output waves resulting from theincoming waves shown in Fig. 3 when tube 8 is biased to operate atapproximately the cutoff point on the Ey-Jp curve, or slightlytherebelow so that the negative half of the incoming wave does notaifect the output circuit.

Fig. 5 illustrates the IR drop across the resistance l5 due to theoutput of rectifier l8. It Will be observed that the drop due to normalsignal amplitude at in Fig. 3 is negligible while the drop due toexcessive amplitude b of Fig. 3 is shown at e to have a large value.

Fig. 6 shows the resultant voltage on plate M (Fig. 1) or grid 22 (Fig.2) when the IR drop developed in the rectifier circuit is properly poledand the amplitude of the static surge is very large, the negative valueof that voltage being indicated at 1.

Fig. '7 illustrates the wave in the output of the tube for normal waveamplitudes at g and for excessive amplitudes at h, when the circuits areproperly adjusted. It will be noted that the wave at g is unchanged onthe positive half while the negative half is suppressed. When anexcessive surge arrives the output builds up to normal or, due to aslight time delay in the circuit, a little above the normal value atwhich time the IR drop produced by the rectifier current is impressedand the amplitude of the output wave drops to zero until the incomingwave again reaches substantially normal value when the output builds upto approximately the amplitude reached before the suppressing actionbecame effective. The fundamental wave is thus chopped into two waves ofvarying base line length and represents very little power at thefundamental frequency in the output circuit of the stage. If thecoupling between the control stage and the one following be tuned, suchharmonics will be efiiciently filtered out and prevented from passingthrough the subsequent stages.

The invention herein described and claimed may be used and/ormanufactured by or for the Government of the United States of Americafor governmental purposes without the payment of any royalties thereonor therefor.

I claim:

1. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, and an anode, and an inputcircuit operatively associated with said tube, of means to feed signalenergy to said input circuit, a nonlinear amplifying device outside thesignal channel through said receiver connected to said means, a dioderectifier, a resistance in series between the electrodes of saidrectifier and also in series in the anode supply of said tube, and meanscoupling the output of said amplifier to the anode of said rectifier.

2. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, and an anode, and an inputcircuit operatively associated with said tube, of a nonlinear amplifyingdevice outside the signal channel through said receiver connected todivert a portion of the signal energy from said channel ahead of saidstage, a diode rectifier, a resistance in series between the electrodesofsaid rectifier, and also in series in the anode supply of said tube,and means coupling the output of said amplifying device to the anode ofsaid rectifier.

3. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, and an anode, and an inputcircuit operatively associated with said tube, of a nonlinear amplifyingdevice outside the signal channel through said receiver connected todivert a portion of the signal energy from said channel ahead of saidstage, a diode rectifier, an impedance in series between the electrodesof said rectifier, and also in series in the anode supply of said tube,and means coupling the output of said amplifying device to the anode ofsaid rectifier.

4. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, an accelerating grid and ananode, and an input circuit including a secondary inductance operativelyassociated with said tube, of means including a primary inductancecoupled to said secondary inductance to feed signal energy to said inputcircuit, a non-linear amplifying device outside the signal channelthrough said receiver connected to said primary, a diode rectifier, aresistance in series between the electrodes of said rectifier, and alsoin series with said accelerating grid, and means coupling the output ofsaid amplifying device to the anode of said rectifier.

5. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, an accelerating grid and ananode, and an input circuit including a secondary inductance operativelyassociated with said tube,

of means including a primary inductance coupled to said secondaryinductance to feed signal energy to said input circuit, a non-linearamplifying device outside the signal channel through said receiverconnected to said primary, a diode rectifier, an impedance in seriesbetween the electrodes of said rectifier, and also in series with saidaccelerating grid, and means coupling the output of said amplifyingdevice to the anode of said rectifier.

6. The combination with a radio receiver stage that includes a vacuumtube having a cathode, a control grid, an accelerating grid and ananode, and an input circuit operatively associated with said tube, of anon-linear amplifying device outside the signal channel through saidreceiver connected to divert a portion of the signal energy from saidchannel ahead of said stage, a diode rectifier, a resistance in seriesbetween the electrodes of said rectifier and also in series with saidaccelerating grid, and means coupling the output of said amplifyingdevice to the anode of and an input circuit operatively associated withsaid tube, of a non-linear amplifying device outside the signal channelthrough said receiver connected to divert a portion of the signal energyfrom said channel aheadof said stage, a diode rectifier, an impedanceinseries between the electrodes of said rectifier and also in series withsaid accelerating grid, and means coupling the output of said amplifyingdevice to the anode of said rectifier. Y

8. A method of controlling noise in a radio receiver including a signalchannel having a vacuum tube that includes a plate electrode, comprisingthe steps of diverting a portion of the signal energy from the signalchannel through the receiver, non-linearly amplifying said portion,applying the resultant amplified portion to produce a unidirectionalcurrent when said amplified portion has an amplitude in excess of apredetermined value, utilizing said unidirectional current to produce apotentiai drop, and applying said drop to reduce the positive biasvoltage on the said plate.

9. A method of controlling noise in a radio receiver including a signalchannel having a vacuum tube that includes a plate electrode, comprisingthe steps of diverting a portion of the signal energy from the signalchannel through the re-.

ceiver, non-linearly amplifying said portion, applying the resultantamplified portion to produce a potential drop proportional to theamplitude of said amplified portion above a predetermined value, andapplying said potential drop to the said plate to reduce the positivebias on said plate.

PHIL]? M. HAFFCKE.

